1. Field of the Invention
The present invention generally relates to broaching machinery, such as the type used to progressively broach blind splines on a workpiece. More specifically, the invention relates to a drive mechanism for converting a rotary movement into a reciprocating rectilinear movement of variable amplitude for driving the ram of a blind spline broaching machine. It will be appreciated, however, that the drive mechanism is capable of broader applications and could be used for many other type of machines.
2. Description of the Prior Art
The broaching of external or internal splines has been practiced with considerable success with long pull broaches which are pulled entirely through the blank in order to complete the spline in a single pass. However, in some cases, workpiece configurations are such that they do not lend themselves to situations where broaches can be pulled entirely through the blank as is the case of an internal spline on a workpiece with directed webs for flanges which will not permit the passage of the broaching tool, see FIG. 1. Also, with respect to an external spline on the end of a shaft, it is not feasible to use a pull broach and, accordingly, such operations must be accomplished by machining, hobbing, or shaping to complete an external spline on the end of a shaft. Accordingly, "blind spline" broaching machines are used in the machining of splines on a workpiece such as the end of a shaft, where the part configuration is such that a pull broach cannot be passed completely over or through the part. Blind spline broaching machines are also suitable for forming other precision features, such as sprockets, keyways, gears, cams and contours. This type of broaching is particularly advantageous in the manufacture of precision parts in terms of machine time, which can be more than ten times faster than the conventional operations of hobbing or shaping.
Conventionally, blind spline broaching consists of the movement of a workpiece through a series of tools which progressively remove material until the desired final dimensions are achieved. Typically, a workpiece is mounted to an indexing table which indexes the workpiece to each of a number of tools held in hydraulic rams. When its respective ram is actuated, a tool performs work on a workpiece, removing a specified amount of metal from the workpiece. The table is then indexed to align the workpiece with the next tool, and the cycle is repeated until the workpiece has encountered each tool and has been brought to its final size and shape. Alternatively, it is known to locate the tools on the indexing table while mounting the workpieces on the hydraulic rams. An advantage here is that the number of hydraulic rams required is independent of the number of broaching operations desired. For instance, six broaching tools can be located on the indexing table while two rams, each holding a workpiece, can be actuated to broach the workpiece using two of the six tools. The table can then be indexed to align the next two tools with the workpieces until each workpiece is finished. The finished workpieces are then removed from the blind spline broaching machine in a preferably automated manner. By definition, blind spline broaching machines require careful control of the stroke of the ram in order to avoid interfering with the remainder of the workpiece. Accordingly, the end of travel for the ram generally occurs within a groove placed on the shaft or internal bore so that the tooth form of the spline can be completed yet the ram may be timely stopped and retracted without interfering with the remainder of the workpiece.
Because efficiency is increased when more than one workpiece is being broached at any given time, it is generally preferable to have more than one ram. However, to maintain the size and complexity of a blind spline broaching machine, it is also preferable to limit the number of rams. An illustrated example of this aspect is illustrated by the prior art blind spline broaching machine shown in FIG. 2. FIG. 2 is an overhead view of an indexing table 112 of a blind spline broaching machine 110. The indexing table 112 has six tool stations at 114 (stations 114a-114f) located along its periphery, along with two receptacles, referred to as "nests", 116a and 116b for loading and unloading workpieces from the indexing table 112. Two hydraulic rams 118 are located above the indexing table 112 as indicated. The hydraulic rams 118 are diametrically opposed each other, and define two separate paths which workpieces can take through the blind spline broaching machine 110. For example, workpieces can pass through the blind spline broaching machine 110 by entering at a first loading station 120 and exiting at the first unloading station 122. Correspondingly, a second loading station 124 is located diametrically opposite the first loading station 120, at which other workpieces can enter the blind spline broaching machine 110. The second group of workpieces will exit the blind spline broaching machine 110 at a second unloading station 126, which is diametrically opposite the first unloading station 122. During a machining cycle, workpieces are loaded into the second nest 116b each time the second nest 116b is indexed to one of the load stations 120 and 124. Concurrently, a workpiece is held by each hydraulic ram 118 and with each movement of the indexing table 112, the workpieces will be driven downwards to encounter one of the tools 114 on the indexing table 112. Once a workpiece has been broached in the last operation by the last tool 114f, the indexing table 112 is again indexed to permit the workpiece to be dropped into the first nest 116a. The subsequent indexing of the indexing table 112 will carry the machined workpiece toward one of the unload stations 122 or 126 while bringing the new workpiece into alignment with the hydraulic ram 118. The new workpiece will then be automatically secured to the hydraulic ram 118 and, with the next movement of the indexing table 112, will be machined by the successive tools 114a-114f, starting with the tool station 114a and continuing through completion at the tool station 114f.
The above described indexing system has significantly reduced the congestion surrounding a prior art broaching machine and the associated loading/unloading activity. The improved indexing table has a single loading/unloading station at which workpieces are alternately loaded into and unloaded from a platform. Because the workpieces are loaded and unloaded from the same position along the periphery of the blind spline broaching machine indexing table, the side of the blind spline broaching machine opposite the loading/unloading station remains open to permit ready access to the tooling and the interior structure of the blind spline broaching machine if such access is necessary. The improved loading/unloading station is described in detail in U.S. Pat. No. 5,315,750 assigned to the common assignee hereof and is herein incorporated by reference.
The use of hydraulic rams associated with the processing of workpieces in a blind spline broaching machine has been accomplished with some success in the prior art. Typically, the hydraulic ram consists of a piston-cylinder combination extending above the frame of the machine. The piston rods are connected to ram slides in combination with re-circulating pre-loaded ball type guides in order to power the slides to regulate their stroke. The tool ram slide and the work holder station on the indexing table are arranged to register upon proper indexing of the table so that different tool collars can each perform a spline cut on a workpiece as the slides are moved vertically down over the retained workpieces. In the prior art, the tool slides may be operated individually, sequentially or simultaneously. Sequential operation requires less hydraulic pump capacity and is more economical than if all the hydraulic rams are operated simultaneously. The operation of the hydraulic ram requires a hydraulic circuit wherein a pump delivers pressure fluid from a tank to a valve having an operating lever which can be manually or solenoid operated. The pressure line delivers fluid to the respective cylinders when the valve is actuated to force the rams down and cause the spline tools to perform respective cuts on a workpiece. Shifting a lever to an opposite direction will direct pressure to a return line in order to raise the rams to permit indexing of the table. Accordingly, the use of hydraulic rams to power a blind spline broaching machine requires extensive hydraulic circuitry as well as separate hydraulic containers to ensure the integrity of the fluid level in the system including numerous valves, all subject to leakage or malfunction. Such hydraulic equipment consumes a great deal of energy and generates excessive heat in the environment which must be removed through air conditioning to provide a comfortable workplace and, in effect, results in a very inefficient operation with respect to the overall efficiency of the operation of a blind spline broaching machine. Further, leakage of hydraulic fluid becomes an environmental problem and any spills must be properly cleaned. A continuous supply of hydraulic fluid must be provided to prevent the broaching machine from malfunctioning due to insufficient hydraulic fluid within the system that controls the operation of the hydraulic rams. These shortcomings and others are well known. To avoid these problems, what is needed is a faster, more reliable mechanical drive for a blind spline broaching machine which overcomes the disadvantages associated with the use of hydraulic rams in powering a blind spline broaching machine.
Numerous mechanical drive systems are known to exist in the prior art to provide straight-line motion for a tool such as a broach yet utilize rotary as well as reciprocating input for the primary motive power. For example, a two bar toggling mechanism such as that disclosed in U.S. Pat. No. 3,623,389 is a common design element to obtain reciprocating linear motion such as is dictated by the operation of a blind spline broaching machine. The ram is slidably guided by the frame for vertical movement and at one end is attached to a toggle link which is pivotally supported at its upper end to the frame of the machine. A central pin of the toggle link is secured to a piston rod of a hydraulic fluid actuator. The hydraulic actuator through its attachment through the toggle link provides reciprocating linear motion to toggle the link from a maximum to a minimum position providing linear reciprocating motion for the ram of the machine.
A further example of a rotary-to-reciprocating movement is taught by Desai et al., U.S. Pat. No. 3,817,139, which discloses a drive arrangement, including a linkage system having a first link pivotally connected between the press slide, and a second link that is connected to a driven crank. A third link is pivotally connected between the press frame and the second link. The several links are arranged to provide desirable kinematic and dynamic characteristics for a shearing press by developing a selected coupler curve at the pivot point between the first and second links, which coupler curve defines the movement of the slide, and accordingly the shearing blade, through the stroke of the slide. In the operation of a mechanical drive linkage system both of these prior art devices generate significant side loads, since the linkage system operates at an angle relative to the linear movement of the ram. When viewed in the context of the requirements of a blind spline broaching machine, which may require as high as forty tons of force to complete a cycle, both these prior art devices are completely inappropriate for such application. Accordingly, what is needed is a mechanical drive mechanism that overcomes the shortcomings of hydraulic drive mechanisms as well as that eliminates side loads, with a minimum deflection, on the drive linkage itself by distributing the loads into the machine structure of a blind spline broaching machine rather than the drive elements themselves.